A semiconductor wafer, shown in FIG. 1 to which reference is made, is formed of a multiplicity of dies 10 each of which is to become an integrated circuit chip. Once manufacturing of the wafer and the circuits thereon is finished, a saw rotates a thin dicing blade, containing miniature diamonds, along the vertical and horizontal "streets" 12 between the dies 10, thereby separating each die 10 from its neighbors. The individual dies are then encapsulated.
The saw has to be properly aligned to ensure that the cut occurs only within the relevant street 12; otherwise, the integrated circuit die 10 will be ruined. The blowup portion of FIG. 1 illustrates two dies 10A and 10B and the cut 14 therebetween. Cut 14 has two edges 16A and 16B, known as "kerfs", which typically are similar to each other. Each kerf 16 is formed of "sawing chips" 18 which are indentations caused by the breaking of the wafer in response to the chipping action of the saw blade. As long as the kerfs 16 are sufficiently far away from the relevant die 10, the cut is acceptable. However, if a crack or "sawing chip" 18, such as sawing chip 18A, is too close to the outer edge of the die 10, the corresponding die (e.g. die 10B) is disqualified.
There are additional complications. Due to the continual need to save "real estate" on the semiconductor wafer, the width of the streets 12 is continually narrowing, reducing the available margin of error. Furthermore, the streets 12 are often utilized for test pads and trial lithography which are sacrificed during the dicing. The portions of the lithographic elements remaining after dicing look similar enough to sawing chips that a die could be incorrectly disqualified.
FIG. 2 illustrates an exemplary cut having sawing chips and lithography lines. The elements marked with reference numeral 20 are lithography lines and those marked with reference numeral 22 are sawing chips. It will be appreciated that lithography lines 20 are not very different than sawing chips 22, especially if the lithography lines 20 are even shorter than those shown in FIG. 2. The sawing chip marked by 22A is too close to the die, labeled 10C.
Inspection is performed in a number of ways. Dicing saws typically are equipped with vision capabilities designed for machine set-up (e.g. for aligning the saw blade along the streets 12). Since the dicing operation is performed under a stream of water, the kerf can only be viewed once the water stream is stopped and the wafer dried. For proper inspection, the wafer must be brought to a microscope and the microscope directed to the kerf areas. This process adds time and, since the sawing vision system cannot differentiate between lithographic lines and sawing chips, this operation is only marginally effective.